1. Field of the Invention
The present invention relates to a novel gene, IbENOD93, and transgenic plants using the same.
2. Description of the Related Art
In most dicotyledonous plants, the primary root develops from the seed at the beginning of growth, and the taproot develops from the primary root. In some plants such as ginseng, carrot, radish, etc., taproot-type storage roots are formed by secondary thickening growth due to continuous cell division and differentiation after the development of the primary root. The taproot-type storage roots store a large amount of carbohydrate that is an energy source for humans and animals, serve as a source of food fiber that is essential for human well-being life and, at the same time, produce secondary metabolites as raw materials for health supplements, which are thus considered economically important.
Meanwhile, in most high-value storage root crops such as ginseng, etc. the storage roots grow underground over several years. During the growth period, the storage roots are exposed to various pathogenic fungi, and thus their cultivation is likely to be stopped due to root rot disease before harvest time. Particularly, it is known that the cultivation of about 50% of storage roots is stopped due to root rot disease in cultivated fields of six-year old ginseng that is a typical high-value root crop in Korea. To minimize the damage to the cultivation of storage root crops, there is a need to develop the breeding of cultivars resistant to root rot disease as well as a molecular breeding method that can shorten the cultivation period of storage roots. Mining of genetic resources involved in the development of storage roots and a study on functional characterization of the genetic resources are prerequisites for the molecular breeding.
Recently, most of the molecular studies on the taproot-type storage roots have been focused on the isolation and characterization of genes involved in the synthesis of high-value secondary metabolites produced in taproot-type storage roots such as ginseng or carrot (Jung et al., 2003. Plant Cell Reports 22:224-230; Choi et al., 2005. Plant Cell Reports 23:557-566; Tansakul et al., 2006. FEBS Letter 580:5143-5149; Just et al., 2007. Theoretical and Applied Genetics 114:693-704; Clotault et al., 2008. Journal of Experimental Botany 59, 3563-3573; Sun et al., 2010. BMC Genomics 11:262; Han et al., 2011. Plant and Cell Physiology. 52:2062-2073, 2012 Plant Cell Physiol. 53:1535-1545; Li et al., 2013. BMC Genomics 14:245). However, the molecular mechanism involved in the development of taproot-type storage roots has not been reported, and the related genes have also not been found. Therefore, the molecular breeding to regulate the development of taproot-type storage roots has not been achieved.
The storage roots are divided into taproot-type storage roots such as carrot, ginseng, radish, etc. and tuberous storage roots such as sweet potato, which are different from each other in their shapes and development processes. The thickening growth of taproot-type storage roots such as carrot is caused by the continuous division in the vascular cambium of the primary roots, during which the secondary vascular tissue is formed, and the cortex and epidermis outside the secondary vascular tissue are peeled off. Therefore, most of the mature taproot-type storage roots consist of the secondary vascular tissue. Meanwhile, unlike the development process of taproot-type storage roots, the thickening growth of tuberous storage roots such as sweet potato is achieved by the development of several abnormal secondary vascular tissues in the primary vascular tissue. However, these storage roots of two types, which are different from each other in their shapes and development processes, are the same in that active cell division occurs in the vascular cambium during the thickening growth.
With the recent development of various molecular approaches, genes have been found that are believed to be involved in the development of storage roots of sweet potato, and as a result, genes have been identified that exhibit differential expression patterns in developing storage roots of sweet potato. (You et al., 2003, FEBS Letters 536, 101-105; Tanaka et al., 2005, Journal of Plant Physiology 162, 91-102; Tanaka et al., 2008, Journal of Plant Physiology 165, 1726-1735). However, the functional characterization of these genes involved in the development of storage roots has not been performed. Recently, the present inventors have found that the SRD1 gene, a MADS-box gene of sweet potato, promotes the cell division in the cambium and metaxylem of storage roots and thus is involved in promoting the thickening growth of storage roots (Noh et al., 2010, Journal of Experimental Botany 61: 1337-1349) and that the IbEXP1 gene inhibits the cell division in the cambium and metaxylem of storage roots and thus is involved in suppressing the thickening growth of storage roots (Noh et al., 2013, Journal of Experimental Botany 64:129-142). It is expected that these sweet potato genes will be used as genetic resources that can regulate the development of taproot-type storage roots such as carrot, etc.
Therefore, there has been a continuous demand for the production of early-maturing transgenic root crops using genes involved in the development of storage roots to increase the productivity of storage roots.
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosures of cited papers and patent documents are entirely incorporated by reference into the present specification, and the level of the technical field within which the present invention falls and details of the present invention are explained more clearly.